Endoscopes are known which are constituted essentially by a rigid probe for insertion into a dark cavity and fitted with means for illuminating an object to be inspected and with optical means for providing the user with an image of the object. In general, the optical means comprise a distal objective lens for forming an image, an image transmission means formed by a series of lenses, and a proximal eyepiece lens which can be moved longitudinally to adjust the focus of the image observed by the user. The optical means are preferably designed in such a manner that the image transmitted through the eyepiece lens is not inverted relative to reality. The lighting means generally comprise a bundle of optical fibers having a distal end located close to the distal objective lens in order to illuminate the object, the bundle of fibers being connected at its proximal end to a light source.
Axial-viewing endoscopes exist in which the optical axis of the distal objective lens coincides with the longitudinal axis of the endoscope. The lighting means of such endoscopes are constituted by a bundle of optical fibers having a distal end that generally forms a illuminating ring around the distal objective lens.
Endoscopes are also known with deflected viewing, in which the optical viewing axis is inclined relative to the longitudinal axis of the endoscope. The optical observation means of such an endoscope comprise a distal deflecting prism which is generally a prism that reflects the image unidirectionally, where such a prism is generally referred to as a “partial reflection prism”. Under such circumstances, the image transmission means mounted in the endoscope generally include a proximal correcting prism which rectifies the inverted image supplied by the distal deflecting prism.
The lighting means of an endoscope with deflected distal viewing are generally constituted by a bundle of optical fibers having a distal end with a bend so as to constitute a lateral lighting window between the distal deflecting prism and the distal end of the endoscope, with the lighting axis being substantially parallel to the viewing axis.
The lighting optical fibers are glass fibers capable of transmitting the spectral components of white light as applied by a light source such as a quartz iodine lamp or a xenon lamp, without significant attenuation of the light. Such lighting means are unsuitable for transmitting ultraviolet light as produced, for example, by a mercury vapor lamp; and in order to transmit ultraviolet radiation it is necessary to use fibers made of quartz or of a suitable plastics material, or indeed a liquid conductor (a sheath filled with an appropriate liquid that is transparent to ultraviolet radiation), such light conductors possessing a degree of rigidity and not enabling their distal ends to be bent with a radius of curvature that is small enough to enable them to be mounted in an endoscope.
In the prior art, this problem has been solved by associating an axial viewing endoscope with an ultraviolet light conductor and a distal endpiece including a deflector mirror. However that solution is not very satisfactory because of the limited optical field and because of the degradation over time of the efficiency with which ultraviolet light is reflected by the mirror, dirt and mirror defects leading to losses of energy that do not enable an object to be illuminated with sufficient intensity and which impede observation by returning a fuzzy image of the illuminated object.